When the disorder is caused by a certain genetic defect, MRI may spot brain abnormalities, researchers say

By Amy NortonHealthDay Reporter

TUESDAY, Aug. 8, 2017 (HealthDay News) -- People with a particular genetic cause of autism show structural abnormalities in the brain that are readily detected with noninvasive imaging, according to a new study.

Using MRI brain scans, researchers found clear brain structure abnormalities in people with autism caused, in part, by defects in chromosome 16.

Those MRI findings were, in turn, related to particular impairments, such as problems with communication and social skills.

It all suggests that brain imaging could one day be used to spot young children most in need of therapy for an autism spectrum disorder, the study authors said. It's estimated that one in 68 U.S. children is "on the spectrum," and symptoms usually appear early in life.

The study included 158 people who carried either of two defects in chromosome 16 that raise the risk of autism.

The flaws are found in a small piece of the chromosome known as p11.2. In some cases, people are missing the p11.2 portion -- which is known as a deletion. In other cases, there is an extra copy of it (known as a duplication).

Together, the defects are thought to contribute to less than 1 percent of all autism cases, said Dr. Elliott Sherr, the senior researcher on the study.

Sherr's team found that p11.2 deletions and duplications were each linked to specific brain structure abnormalities that were visible on MRI.

People with a deletion had excess tissue near the brain stem, and a thick, abnormally shaped corpus callosum -- a bundle of fibers that connects the left and right sides of the brain.

In contrast, people with a p11.2 duplication had a thin corpus callosum and "undergrowth" in certain other areas of brain tissue.

"Their brains look very different," said Sherr, a professor of neurology at the University of California, San Francisco.

And those structural abnormalities appear to correlate with different types of impairments, the study found.

The MRI findings in deletion carriers were tied to problems with communication and social skills. Meanwhile, the findings in duplication carriers were linked to lower IQ scores and problems with verbal skills.

What does it all mean? It's not clear yet, Sherr said.

"What we can say is, there's a strong link between these anatomical features of the brain and people's behavior," he said.

In general, people with p11.2 deletions or duplications have "intellectual challenges," such as lower-than-normal IQ, Sherr explained.

But they do not all develop autism, he said. The risk is thought to be 20 to 25 percent.

The current findings, Sherr said, raise the question of whether MRI could help identify young children likely to need therapy for autism.

First, though, important questions would need to be answered, he noted.

The current findings are based on one-time brain scans of people who ranged in age from 1 to 63 years. So it's not clear whether the MRI findings predict future impairments in people who carry the p11.2 abnormalities.

"We'd like to find out whether we can see these brain changes early in development," Sherr said. "And if we do see them, do they point to the risk of developmental challenges later on?"

He said studies like this are important because they help reveal the biology underlying autism.

"And that might point us to new therapies," Frazier said.

In general, experts believe that autism arises from a perfect storm of conditions. A child has some type of genetic vulnerability, then is exposed to one or more environmental factors during early development that, together, lead to autism.

At this point, Frazier said, researchers have found nearly 100 genes believed to contribute to autism risk.

Some genetic flaws -- like the chromosome 16 defects -- have a "major effect," Frazier said. But they, alone, are still not enough to cause autism.

If researchers can figure out why certain people with chromosome 16 defects develop autism, Frazier said, that could give insight into autism more generally.

As it stands, the chromosome 16 abnormalities are detected only if genetic tests are done after an autism diagnosis has been made based on behavior, Frazier said.

Still, researchers are interested in whether MRI can be used to "predict" autism risk in certain young children, Frazier said.

One recent study focused on babies who were at heightened risk because a sibling had autism. It found that early brain differences did show up on MRI, and accurately predicted a future autism diagnosis 80 percent of the time.

But, Frazier said, more work is needed to verify those findings.

The new study was published online Aug. 8 in the journal Radiology.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more on autism.